In modern semiconductor wafer processing for the manufacture of transducer structures with integrated electronics, structures are employed that have extremely thin cross-sectional areas that are often designated as membranes. Such structures include diaphragms and cantilever beams such as those employed in pressure transducer or similar semiconductor devices. These extremely thin membrane-like structures are in themselves difficult to fabricate using prior art semiconductor techniques. Moreover, these thin membrane-like structures are generally fabricated after active elements are formed on the wafer.
Furthermore, when semiconductor transducer structures include amplifiers, signal conditioners and like elements, these elements must be formed on the active side of the wafer where the stress sensing elements of the transducer are formed. Ideally, these thin membrane elements should be formed prior to the fabrication of the amplifier elements, the signal conditioning elements, and the sensor elements. However, prior art fabrication techniques generally require the thin membrane-like structures to be fabricated after the other elements are diffused or deposited onto the surfaces of the wafer. This is because the thinning techniques used for fabricating these thin membrane-like structures involve high temperature etching techniques which employ materials such as NaOH or KOH or other conductivity selective etches. These thinning techniques are known to degrade the elements formed on the active side of the membrane structure.
These adverse effects can be substantially avoided if these thin membrane-like structures were fabricated before the formation of the active elements. However, because these membrane-like structures are very fragile, breakage resulting in low yields becomes a major difficulty when active elements are fabricated on these thin membrane-like structures.
It is, therefore, an object of the present invention to provide a method for fabricating thin membrane-like structures before the formation of the active elements which avoids the breakage and low yields associated therewith.